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<h1>getAlphaFilter</h1>
<p class="purpose">Create filter for <code>medium.alpha_filter</code>.</p>

<h2>Syntax</h2>

<pre class="codeinput">
alpha_filter = getAlphaFilter(kgrid, medium, filter_cutoff)
alpha_filter = getAlphaFilter(kgrid, medium, filter_cutoff, taper_ratio)
</pre>

<h2>Description</h2>
<p><code>getAlphaFilter</code> uses <code><a href="getWin.html">getWin</a></code> to create a Tukey window via rotation to pass to the <code>medium.alpha_filter</code> input field of the first order simulation functions (<code><a href="kspaceFirstOrder1D.html">kspaceFirstOrder1D</a></code>, <code><a href="kspaceFirstOrder2D.html">kspaceFirstOrder2D</a></code>, and <code><a href="kspaceFirstOrder3D.html">kspaceFirstOrder3D</a></code>). This parameter is used to regularise time reversal image reconstruction when absorption compensation is included.</p>

<h2>Inputs</h2>

<table class="body">
    <tr valign="top">
        <td width = "150"><code>kgrid</code></td>
        <td>k-Wave grid object returned by kWaveGrid</td>
    </tr>  

    <tr valign="top">
        <td><code>medium</code></td>
        <td>k-Wave medium structure</td>
    </tr>    
    
    <tr valign="top">
        <td><code>filter_cutoff</code></td>
        <td>
            <p>alpha_filter cutoff frequency [Hz], where</p>
            <p><code>filter_cutoff = [f_all]</code> in 1-D<br/><code>filter_cutoff = [f_all]</code> or <code>[f_x, f_y]</code> in 2-D<br/><code>filter_cutoff = [f_all]</code> or <code>[f_x, f_y, f_z]</code> in 3-D</p>
	    <p>Any of the filter_cutoff inputs may be set to <code>'max'</code> to set the cutoff frequency to the maximum frequency supported by the grid</p>
        </td>
    </tr>
          
</table>

<h2>Optional Inputs</h2>

<table class="body">
    <tr valign="top">
        <td width = "150"><code>taper_ratio</code></td>
        <td>taper ratio for Tukey Window (default = 0.5)</td>
    </tr>     
          
</table>

<h2>Outputs</h2>

<table class="body">
    <tr valign="top">
        <td width = "150"><code>alpha_filter</code></td>
        <td>filter</td>
    </tr>      
</table>

<h2>Examples</h2>
<ul>
<li><a href="example_pr_2D_tr_absorption_compensation.html">Image Reconstruction With Compensation For Acoustic Absorption</a></li>              
</ul>

<h2>See Also</h2>

<code><a href="getWin.html">getWin</a></code>, <code><a href="kspaceFirstOrder1D.html">kspaceFirstOrder1D</a></code>, <code><a href="kspaceFirstOrder2D.html">kspaceFirstOrder2D</a></code>, <code><a href="kspaceFirstOrder3D.html">kspaceFirstOrder3D</a></code>




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